Studies of defects in photonic materials

Indium tin oxide (ITO) films have high optical transmission and infrared reflectance, good electrical conductivity, excellent substrate adherence, hardness and chemical inertness. These properties lead to many applications in the area of photonics. Bombardment of ITO films with 1 MeV protons has been carried out resulting in an observed darkening. Insights into the darkening mechanism that consists of three growth stages as a function of fluence are provided by a study of the optical absorption and X-ray lattice parameter. A new interpretation is provided for the darkening mechanism in terms of the production of defect clusters resulting from the atomic displacements during implantation. CsI crystals are very effective scintillator materials for particle detectors in high energy physics. Although radiation hard, radiation damage produces colour centres in CsI that reduce light emission and can negatively affect the luminescent centres. Using a combination of Raman and optical absorption spectroscopy applied to CsI crystals bombarded with 1 MeV protons at 300 K, the resulting defects are shown to be F-type centres and interstitial V-centres having the I3- structure and being responsible for absorption bands at 2.7 and 3.4 eV. Isochronal and isothermal annealing experiments show a mutual decay of the F and V-centres. The results are discussed in relation to the formation of interstitial iodine aggregates of various types in alkali iodides.